Method of producing highly lustrous hollow bodies from cellulose products and other substances



P 1941- K. BRATRING 2,254,263

' METHOD OF PRODUCING HIGHLY LUSTROUS HOLLOW BODIES FROM CELLULOSEPRODUCTS AND OTHER SUBSTANCES Filed 001.- 15, 1958 INVENTOR K027 5/34rAv/ve ATTORNEY Patented Sept. 2, 1941 TROUS HOLLOW BODIES FROM CELLU:LOSE PRODUCTS AND OTHER SUB- STANCES Kurt Bratring, Dahlem, Berlin,Germany, assignor to Neocell Products Corporation Application October15, 1938, Serial No. 235,240

In Germany May 7, 1 936 I V 3 Claims. (CI. 1858 The invention of mypresent application, which is a continuation in part of my formerapplication Serial No. 140,768, filed May 4, 1937, relates to theproduction of hollow articles by d pping a mold in a clipping bathcontaining a solution or suspension of some plastic substance, such forexample as either nitrocellulose or other cellulose esters or celluloseethers, or natural resin (amber) or synthetic resin, as for examplepolystyrol, all with or without additions of other materials. I havefound it particularly useful in the manufacture of articles of celluloseacetate by dipping the molds in a solution of cellulose acetate inacetone. It is the object of my invention to produce such bodies in ahighly lustrous condition, and to preserve the natural transparency ortranslucency of the material unimpaired.

It has been suggested that a hollow article of Celluloid may be formedby dipping a hollow soft-rubber core into a solution of gelatine andwater, allowing it to harden for about one minute, dipping in thecellulose solution to form the article, drying, and then immersing themold so formed with the formed article upon it in a bath f warm water tosoften the gelatine and to allow the article to be removed from thecore. It is, however, impossible to produce formed articles havingsmooth interior surfaces in this way, because the acetone, or any othersolvent of Celluloid known to me, will immediately attack the softgelatine coating produced as above described and give it a rough andporous surface, which surface will of course be reproduced in the formedarticle. Further, the temperature of the Water required to suflicientlysoften the gelatine is so high, being around 60 C., as to causedeformation of the finished article, which is highly objectionable,particularly in the production of a number of articles intended to be ofuniform size. Further, it is almost inevitable that a certain amount ofacetone will exist in the article at that stage of the process where itis removed from the mold; unfortunately in a bath of water at, around orabove 60 C. a reaction takes place between this acetone and the articlewhich gives the article a cloudy, milky appearance.

It has also been proposed to form articles of Celluloid by dipping solidcores covered with a coating of parafiin, stearine, Vaseline or similarsubstance into a bath containing Celluloid in solution, drying, andremoving the formed article by heating to a temperature high enough tomelt the coating. But here also the solvent will in-.

evitably attack the coating and destroy the ,terial such as glass.

smoothness of the surface, so that the formed article will not be smoothon the inside, and therefore not lustrous. Further, the reaction in thedipping bath between the acetone and the hydrocarbon coating results ingiving the article an Opaque appearance, which is in most cases highlyobjectionable, and in the case of articles intended to be transparent,ruinous.

And in general whenever in the past a layer -of material different fromthe material of the finished body has been deposited on a core forpurposes of lubrication, it has always been the practice to employeither material which is normally soft and slippery, or materialdeposited from a solution and used before it is dry and while it isstill slippery. But, to produce finished articles of lustrous surfaceand high quality the surface upon which the article is formed' must besmooth, hard and bone dry during the deposition of the article-formingfilm thereon.

I have found that for the production of highly lustrous formed articlesit is necessary to use cores'with highly polished and lustrous surfaces;such cores are preferably of hard, smooth ma- But such hard cores are sorigid that when the formed article shrinks, as it always does inthedrying process, it adheres so tenaciously'to the core as to make itimpossible to remove the formed article without injury.

My invention is based upon the discovery that it is possible by properchoice andtreatment of the ingredients of my intermediate layer tosecure a mold surface which is extremely smooth and hard during thedeposition of the article-forming film, and with which the solvent inthe immersion bath undergoes no deleterious chemical reaction, and whichyet by the application of moisture and upon being slightly warmedbecomes a slippery intermediate layer admirably adapted to supplylubrication between the core and the finished article upon removal ofthe latter. When such a layer is deposited upon a rigid core, it ispossible to allow the formed article to shrink in "drying, and yet toremove it readily from the 7 article.

In carrying out my invention in the best manner known to me, I, providecores of glass of the proper shape and dip them in a solution whichnormally comprises 100 grams of gelatine, 100 grams of saccharose and 20grams of glycerinc in 800 cubic centimeters of water. The core, with themixture adhering to it, is then subjected to a thorough drying process,until the skin upon the core is bone dry. This drying operation isconducted in air at about 40 to 45 C. for a half of an hour or more. Thecore is thus covered with a very thin, hard, smooth, dry lustrous skin,normally considerably less than one millimeter in thickness. Thereuponthe resulting mold as I call it, consisting of the core with the skinupon it, is dipped in a dipping bathand dried. This operation may berepeated as many times as is necessary to produce a formed article ofthe proper thickness.

The drying operation should be commenced in a cool atmosphere to preventthe formation of bubbles, in accordance with the invention of myapplication Serial No. 218,327, filed July- 9, 1938, which forms no partof the present application and is not herein claimed. It should becontinued at progressively higher temperatures and should be thorough.When the drying operation has been completed, the molds with the formedarticles thereon are immersed in a bath of water at a temperature of 45C. or somewhat lower. The water makes its way between the formed articleand the mold, and by its action, plus the action of the heat, softensthe skin and converts it into a lubricant. Thereupon the formed articlemay readily be removed in any convenient manner; for example, it may beblown off the mold. .by a jet of air forced through a channel inthe'core, in the, manner described in my Patent No. 2,114,794. Theformed article is then washed in warm water and dried. The cores areWashed and used again. The gelatine, glycerine and sugar may berecovered for subsequent use.

I have referred above to the evil effects which result from attemptingto remove articles of this character from the molds on which they areformed, or otherwise treat themfor any substantial time, in water'atorabove the danger temperature, which temperature is in the neighborhoodof 60 (3., these evil effects being:

(1) A deformation of the formed article, so that its final. shape is notthat which it would have had if not so deformed; and

(2) The tendency to milkiness, cloudiness or opacity due to the heatreaction on the formed article of the trace of acetone which is almostsure to be present in the formed article at this stage of the process.

To avoid these evil effects I. keep my water bath Well below the dangertemperature; in order to be able to. do this I make the skin of amaterial which will soften and turn into a lubricant under moist heatwell below the danger temperature. A very simple andefiicacious meansfor producing this result is to make the skin, as described above, of amixture of gelatine and sugar or some other material which will have, asimilar action in reducing the temperature at which gelatine softens.These materials must be neutral to all materials with which the skincomes in contact during the subsequent operations,

Sugar has the additional advantage of greatly relatively small. Thesugar also adds considerably to the smoothness and lustre of the driedskin, and therefore of the formed article, the surface of which isdependent upon the surface of the coating on which it is laid down.

The function of the glycerine is to add to the lubricating properties ofthe skin when it is softened in the warm water bath, thus furtherfacilitating the removal of the formed article from the mold.

The core, which I have hitherto described as being made of glass, may bemade of metal, wood, plaster, synthetic resin, soft rubber or any othermaterial which is not attacked by the materials with which it comes incontact during the dipping operation.

If cores not of themselves highly polished and lustrous are used withoutthe skin above described, as for example cores made of soft rubber, theresulting formed articles are not lustrous. I find, however, that bydipping such cores in the skin-forming solution and drying as abovedescribed, I produce a skin or coating upon the cores which is muchsmoother and more lustrous than the cores themselves, and thereforeleads to the formation of a hollow article of superior lustre, althoughthe hollow articles thus formed are not in general as lustrous as thoseformed on rigid, highly polished cores, as for example cores of glass orhighly polished metal, in the manner above described.

I am of the opinion that in the water bath the skin swells, and byswelling tends to assist the removal of the formed article.

In the drawing attached to the specification, which shows a verticalsection of a core with the intermediate layer upon it and with theformed article deposited in place on the intermediate layer, is thecore, 2 is the intermediate layer and 3 is a formed article dried andready for removal.

I claim:

1'. The method of producing lustrous hollow articles of plasticcomposition which includes forming on a core a thin skin of a materialcapable of being hardened by drying, and of being softened again by theaction of moist heat, which skin is neutral to and not substantiallyattacked or'modified by any material with which it comes in contactduring the subsequent clipping operation, thoroughly drying said skin toprovide a hard, dry, lustrous surface, immersing the mold so formed in adipping bath, thereby producing a hollow article on the mold, drying thearticle, subjecting the mold with the article thereon to the action ofmoist heat at a temperature suiiiciently high to soften the skin, andremoving the hollow article from the mold.

2. The method comprising forming on a hard core a thin, dry, lustrousskin of a composition comprising gelatin, glycerin and sugar by dippingsaid core into a solution of said composition and drying said solutionupon said core, immersing the coated core in a bath comprising asolution of a cellulosic material, removing the core from the bath,drying the cellulosic material upon the core to form a hollow articlethereon, subjecting the core with the article thereon to the action ofmoist heat at a temperature below 60 0., whereby the composition betweenthe core and the hollow article is softened, and removing the hollowarticle from the core.

3. The method of producing lustrous, hollow articles of cellulosicmaterial which comprises forming on a hard core a thin skin of amaterial to form thereon a hollow article, and subjecting the core andthe article thereon to the action of moist heat at a temperature ofapproximately 45 C., whereby said skin is softened and said hollow 5article may be removed from said core.

KURT BRATRING.

